Today’s birthday boy is probably the most notorious of all Renaissance scholars, Girolamo Cardano (24th September 1501 – 21st September 1576) usually known in English as Jerome Cardan or Hieronymus Cardanus. Cardano was a physician, mathematician, astronomer, astrologer, philosopher, engineer, professional gambler and magician who regularly consulted with the spirit of his dead father who had taught him his necromancy. He is regarded by many as the founder of modern algebra, he became the most successful physician in Europe whose medical works were only outsold by those of Andreas Vesalius, he was the most widely read philosophical author of his age and the most highly regarded astrologer who was thrown into prison for casting the horoscope of Jesus and from his prison cell became the Pope’s personal astrologer. There are not many scholars in the history of science, who can rival Cardano. However I am not going to write about Cardano’s scientific and social achievements but about his publishing activities because he shared both his North European editor and publisher with Nicolaus Copernicus.
Now it is well known under historians of science and those who take a strong interest in the subject that Copernicus’ De revolutionibus was edited for the press by Andreas Osiander who added a notorious Ad lectorum [(note) to the reader and not preface as it is often called] to the book explaining that the reader does not have to consider Copernicus’ heliocentric theory as the truth but can regard it as a working hypothesis that mathematical explains the facts more accurately than other hypothesis, i.e. an instrumentalist interpretation. An explanation that contradicted Copernicus’ own views as expressed a couple of pages further on in his preface, where he clearly states that he holds his own heliocentric theory for the truth. What is less well known is that Osiander also edited Cardano’s mathematical books for the press.
As Cardano was still an unknown lecturer in mathematics and a struggling physician without a reputation he tried to improve his financial situation by writing and publishing a practica. This is a mathematical textbook of practical mathematics used by private tutors to teach the fundaments of algebra to apprentice merchants and the basics of geometry to apprentice artist, architects and builders. Such private teaching of practical mathematics was very widespread in the trading cities of North Italy and Southern Germany in the Renaissance and good textbooks enjoyed large sales and good profits for the authors who usually also worked as private maths tutors. In the 16th century there was no wholesale book distribution trade as we know it today and printer publishers such as the Nürnberger Johannes Petreius would take their books to the annual book fairs in Leipzig and Frankfurt, in those days the two largest in Europe, and sell then to other printer publishers who would then offer them for sale in their own towns. Petreius also bought books from his colleagues, which he then offered his customers from his market stall back in Nürnberg. At the Frankfurt Book Fair in 1539 Petreius, who specialised in printing books on the mathematical sciences, came across Cardano’s freshly published Practica, originally published in 1538 in Milano, and was obviously impressed because as soon as he was back in Nürnberg he took up contact with the author or to be more precise Andreas Osiander did so on his behalf. Osiander wrote to the Italian medic offering him the possibility to have his Practica published in Germany by Petreius, who by this time was a large and successful printer publisher with a very good reputation. Cardano did not need to be asked twice and a new improved edition of his Practica soon rolled off the press in Nürnberg to be followed other the years by his entire mathematical, astrological medical and philosophical output; a very profitable partnership for all concerned. The relationship even continued after Petreius’ death in 1550 when his cousin Heinric Petri in Basel took over his publishing list, continuing to publish very successfully further editions of Cardano’s oeuvre as well as the second edition of Copernicus’ De revolutionibus.
Notable milestones in the Petreius, Osiander, Cardano relationship were Cardano’s Libelli duo, unus de supplemento almanach, alter de restitutione. Item geniturae LXVII (1543), which appeared in an expanded edition in 1547 as Libelli quinqz. etc. and his Artis magnae sive de regulis algebraicis lib. unus. (1545). The first is the first printed collection of horoscopes, such horoscope collections were an attempt to show that astrology was an empirical science by demonstrating how the lives of prominent persons were reflected in their birth charts. Such collections were very popular in the 16th century and Cardano’s was the market leader. These collections are today an important historical source in our knowledge and understanding of Renaissance astrology, which was the main driving force behind the development of Renaissance astronomy and are also important general sources for biographical details such as dates of birth that are not noted anywhere else. The second is Cardano’s mathematical masterpiece and is the first comprehensive treatment of algebraic equations and contains the first published general solutions of the cubic and bi-quadratic equations as well as the first tentative, largely negative, analysis of imaginary numbers. Many historians of mathematics regard its publication as the beginning of modern mathematics, a judgement that I don’t necessarily agree with.
Both of these books as well as Cardano’s Practica (two editions 1541 and 1542) were edited for the press by Osiander a small but important fact in the publishing history of the De revolutionibus. Andeas Osiander was a teacher of Hebrew who became a reforming preacher who played a central role in the city state of Nürnberg becoming the first Lutheran protestant state in Germany in 1525. It would appear that Petreius and Osiander first became acquainted through Petreius’ activities as a printer of Lutheran polemic texts. Now a major problem in Osiander’s role as editor of De revolutionibus is that he is not known to have studied mathematics or to have written or published any mathematical works in any form what so ever. The only evidence that we have that Osiander was qualified to carry out this work is the fact that Cardano praises him for his knowledgeable and expert editing of his mathematical, and that also means astrological, works in the preface of his Artis magnae in 1545. Although we still don’t know where Osiander acquired his mathematical skills we do have the testimony of a knowledgeable expert, Cardano, that he did actually possess those skills.